Checking if numbers are even is fundamental for alternating patterns, conditional logic, data grouping, and implementing features like zebra striping or alternating layouts in JavaScript applications. With over 25 years of experience in software development and as the creator of CoreUI, I’ve implemented even number checking extensively in components like table row styling, pagination logic, and layout systems where alternating behaviors enhance visual organization and user experience. From my extensive expertise, the most efficient and mathematically sound approach is using the modulo operator (%) to test divisibility by 2. This method is simple, performant, and directly expresses the mathematical definition of even numbers.